You can drag an object onto another. If they are the same class and not class None then you are prompted "Swap the Objects", if you choose yes then the two objects are swapped with each other. If you choose No then the moved object is left where you dropped it. If you select Cancel then the move is undone

You can also force the Objects to swap even if they are a different class.

To do this start dragging then hold down shift before dropping.